de Valera gave discreet support to Britain in a number of ways. The Irish government supplied weather reports directly to the War Office that proved valuable to the Allies. 

British aircraft were allowed to fly from bases Lough Erne in County Fermanagh across Donegal to the Atlantic. This twenty mile strip, the Donegal Corridor, was used by aircraft searching for German surface ships and U-boats. Further north, aircraft from bases in Derry were also permitted to fly over Donegal. 

Allied aircrew who crash-landed in Irish territory were allowed to return across the border, German airmen who crash landed in Ireland were held in the Curragh internment camp.  

Irish citizens who wished to join the British forces were allowed to leave the country to do so. In the course of the war, some 80,000 men and women from neutral Ireland served in British uniform across the globe.